The semiconductor device (semiconductor equipment) is formed by repeatedly using a photolithography technique in which a photomask in which a circuit pattern is drawn is irradiated with exposure light and the circuit pattern formed in the photomask is transferred onto a semiconductor substrate (semiconductor wafer) through a reduction optical system. The photomask is manufactured by forming a circuit pattern on a substrate on which an optical film is formed (photomask blank). Such an optical film is generally a thin film composed mainly of a transition metal compound or a thin film composed mainly of a silicon compound containing a transition metal, and a film functioning as a light-blocking film or a film functioning as a phase shift film is selected according to the purpose.
The photomask is used as an original drawing for manufacturing a semiconductor element having a micro-pattern and is required to have no defect, which naturally requires the photomask blank to also have no defect. Due to such circumstances, many studies have been made on techniques for defect detection of photomask and photomask blank.
In JP-A 2001-174415 (Patent Document 1) and JP-A 2002-333313 (Patent Document 2), a method in which a substrate is irradiated with laser light and a defect and a foreign matter are detected from scattered reflection of light is described, and particularly a technique in which a detection signal is given asymmetry to discriminate whether a defect is a projected defect (bump defect) or a recessed defect (pit defect) is described. Furthermore, in JP-A 2005-265736 (Patent Document 3), a technique in which deep ultraviolet (DUV) light used for carrying out a pattern inspection of a general optical mask is used as inspection light is described. Moreover, in JP-A 2013-19766 (Patent Document 4), a technique in which inspection light is split into plural illumination spots and is scanned and each reflected beam is received by a light detecting element is described.